Polymer coated carrier particles for electrophotographic developers

Abstract

A coated carrier having a core particle coated with a mixture of an electronegative insulating polymer comprising a polyvinylidenefluoride polymer or copolymer and an electropositive conductive polymer comprising a polymethyl methacrylate polymer or copolymer with a conductive material dispersed therein is made by powder coating. The coated carrier has unique properties, including a conductivity of from 1.1×10 −14 to 1.0×10 −8 mho-cm −1 , a triboelectric charging value of from 12 to 20 and an average particle diameter of from 65 to 75, rendering the coated carrier ideal for use in a developer to be used in a magnetic brush type development apparatus. The powder coating method includes mixing the core particle and the mixture of negatively charging polymer and conductive polymer until the mixture of negatively charging polymer and conductive polymer adheres to the core particle, heating the mixture of the core particle and the mixture of negatively charging polymer and conductive polymer until the mixture of negatively charging polymer and conductive polymer melts and fuses to the core particle, and cooling the coated core obtained.

What is claimed is:  
     
       1. A coated carrier comprising a core particle coated with a mixture of an electronegative insulating polymer comprising a polyvinylidenefluoride polymer or copolymer and an electropositive conductive polymer comprising a polymethyl methacrylate polymer or copolymer having a conductive material dispersed therein, 
       wherein the core particle has an average particle diameter of from 50 to 80 microns, a magnetic saturation of from 80 to 110 emu/g, a coercivity of from 20 to 30 Oer, and a retentivity of from 1.0 to 5.0 emu/g, and  
       wherein the coated carrier has a conductivity of from 1.1×10 −14  to 1.0×10 −8  mho-cm −1 , a triboelectric charging value of from 12 to 20 and an average particle diameter of from 65 to 75 microns.  
     
     
       2. The coated carrier of claim  1 , wherein the core particle is magnetite. 
     
     
       3. The coated carrier of claim  1 , wherein the conductive material is carbon black. 
     
     
       4. The coated carrier of claim  3 , wherein the carbon black is present in the polymethyl methacrylate polymer or copolymer in an amount of from 10 to 30% by weight of the polymer or copolymer. 
     
     
       5. The coated carrier of claim  1 , wherein the mixture of the electronegative insulating polymer and the electropositive polymer contains from 10 to 90% by weight of the electronegative insulating polymer and from 10 to 90% by weight of the electropositive polymer. 
     
     
       6. The coated carrier of claim  1 , wherein the mixture of the negatively charging polymer and the conductive polymer comprises 0.05 to 10% by weight of the coated carrier. 
     
     
       7. The coated carrier of claim  1 , wherein the coated carrier further has a particle size distribution such that 90% of the particles have a diameter greater than 51 microns, 50% of the particles have a diameter greater than 70 microns, 10% of the particles have a diameter greater than 98 microns, and the minimum particle diameter is 30 microns. 
     
     
       8. The coated carrier of claim  1 , wherein the coated carrier further has a bulk density of from 1.85 to 2.75 and a mass flow of from 1.25 to 1.85. 
     
     
       9. The coated carrier of claim  1 , wherein the coated carrier has a conductivity of from 1.1×10 −14  to 1.1×10 −13  and a triboelectric charging value of from 16 to 19. 
     
     
       10. The coated carrier of claim  1 , wherein the coated carrier has a breakdown voltage of 30 to 350 V. 
     
     
       11. A method of making a coated carrier comprising a core particle coated with a mixture of a negatively charging polymer comprising a polyvinylidenefluoride polymer or copolymer and a conductive polymer comprising a polymethyl methacrylate polymer or copolymer having a conductive material dispersed therein, 
       wherein the core particle has an average particle size of from 50 to 80 microns, a magnetic saturation of from 80 to 110 emu/g, a coercivity of from 20 to 30 Oer, and a retentivity of from 1.0 to 5.0 emu/g, and  
       wherein the coated carrier has a conductivity of from 1.1×10 −14  to 1.0×10 −8  mho-cm −1 , a triboelectric charging value of from 12 to 20 and an average particle diameter of from 65 to 75 microns,  
       the method comprising mixing the core particle and the mixture of negatively charging polymer and conductive polymer until the mixture of negatively charging polymer and conductive polymer adheres to the core particle, thereafter heating the mixture of the core particle and the mixture of negatively charging polymer and conductive polymer until the mixture of negatively charging polymer and conductive polymer melts and fuses to the core particle, and subsequently cooling the coated core obtained.  
     
     
       12. The method according to claim  11 , wherein the mixing is by mechanical impaction or electrostatic attraction. 
     
     
       13. The method according to claim  11 , wherein the heating is at a temperature of from 320 to 550° F. for 10 to 60 minutes. 
     
     
       14. The method according to claim  11 , wherein the mixture of the negatively charging polymer and the conductive polymer contains from 10 to 90% by weight of the negatively charging polymer and from 10 to 90% by weight of the conductive polymer. 
     
     
       15. A developer for a printing machine comprising toner and the coated carrier of claim  1 .